The present invention relates to the recovery and recycling of gasses. The methods and devices disclosed are useful in a number of applications including MRI, MR spectroscopy, nuclear medicine scans, computerized tomography scans, PET scans and in anesthesiology.
The value of MRI as a diagnostic tool for respiratory problems can be greatly enhanced if, before imaging, a person inhales a noble gas that has been put into a hyperpolarized state. Unfortunately, the future of hyperpolarized gas imaging is threatened by the limited availability of appropriate noble gasses, primarily 3H and 129Xe, and their high cost (Frosatti, et al., J Low Temp. Phys. 111:521-532 (1998)). Thus, it would be highly advantageous to have a system that can be used to recover and recycle used noble gasses for later use. Ideally, such a system would also be compatible with the recovery of other gasses in a wide variety of applications.
The present invention is based, in its first instance, upon the development of a novel system for extracting hyperpolarized noble gas (including 3He and xenon) after it has been has been administered to a patient undergoing an MRI imaging procedure. The gas is purified and recycled back to the hyperpolarized gas generator or stand-alone pressurized gas source. The system may also be advantageously employed to recover other types of gasses from a variety of sources. For example, it can be used to recover gasses used in connection with medical procedures such as MRI, MR spectroscopy, nuclear medicine scans, computerized tomography scans, PET scans and in anesthesiology. In addition, gasses used for veterinary purposes or in connection with the imaging of materials could be recovered. Examples of gasses that can be recovered include any isotope of Xe; any isotope of He; 31P; 13C; 23Na; and 19F.
In a first embodiment, the invention is directed to a method for recycling a chosen gas after it has been used in, preferably, a medical procedure. For example, a noble gas may be recycled after having been used in diagnostic MRI imaging. The method begins when a mixture containing the chosen gas is collected and introduced into a recycling system. For example, a patient that has undergone MRI imaging may exhale noble gas into a container which is connected to (or may subsequently be connected to) to a recycling system. This system has a pump that passes the collected gas through a series of components, e.g., dryers, filters, getters, and sterilizers, designed to purify the chosen gas. Once purified, the chosen gas is transferred to a storage container where it may be maintained until needed. Upon demand, the stored gas is released and, optionally, mixed with other gasses. The mixture may then be passed into a system component designed to prepare it for administration to a second patient. For example, a noble gas may be introduced into a polarizing chamber where it is put into a hyperpolarized state prior to MRI. Finally, the prepared gas is delivered to a new subject, either directly, or by first introducing into a portable container. This system may be used in connection with any gas and with any of the medical procedures discussed above. In one preferred embodiment, a hyperpolarized gas is continually transported to and from a person during an MRI process. Typically, this will be accomplished by delivering the gas to the person through a port in the bore of the scanner of the machine used for MRI.
In another embodiment, the invention is directed to a device (see, for example, FIG. 1) with multiple components for recycling a chosen gas, e.g. a noble gas. The device may include a first portable container (102) for gas retrieved, e.g. from a patient. This container may be connected to one end of a first gas line and a vacuum pump (106) is connected to the second end. There is a getter (112) connected to the vacuum pump and a storage container (118) is connected to the getter. The design allows the vacuum pump to evacuate the gas from the first portable container and then pass it through the getter and into the storage container. One end of a second gas line is also connected to the storage container and its other end to a mass flow controller (120) for regulating the amount of gas that flows out of storage. The mass flow controller is connected to a purifier (122) which, in turn, is connected to a cell (126) for preparing the gas for future use, e.g., for transforming a noble gas into a hyperpolarized state. Finally, the cell may be connected to a second portable container (124) for receiving the prepared gas. Additional components that may be part of the device include: a dryer (108) connected to the vacuum pump (106); a second purifier (110) connected to the dryer (108) and to the getter (112); a sanitizer (131) for sterilizing gas, which is connected to the getter (112) and to the storage tank (118); a compressor (116) connected to the getter (116) and to the storage tank (118); a surge tank (104) connected to the first portable container (102) and to the vacuum pump (106); a valve (114) for introducing additional gas into the storage tank (118), which is connected to the sanitizer (131) and to the compressor (116); and a second storage tank (130) that may be used to mix additional gasses with chosen gas, which is connected to the purifier (122) and to the mass flow controller (120). In its most preferred form, the device comprises all of the elements discussed above arranged as shown in FIG. 1.
It will be apparent to one of skill in the art that certain of the components of the device described above may be rearranged without substantially interfering with its overall performance. Devices having only nonsubstantive changes of this type are encompassed as part of the invention.
In another embodiment, the invention is directed to a device for recycling a chosen gas, comprising: means for retrieving a mixture of gasses containing the chosen gas and introducing this mixture into the device; means for propelling the gas through the device; means for purifying the chosen gas as it is propelled through the device; means for storing purified gas; means for removing gas from storage and for regulating flow from storage; means for preparing gas for future use; and means for transferring the prepared gas out of said device. In one preferred embodiment, the chosen gas is a noble gas that is prepared for future use by putting it into a hyperpolarized state. The device may be incorporated into an MRI imaging machine and positioned in such a manner that the retrieval of used gas occurs at an exit port in the bore of the scanner of the MRI machine and gas is transferred out of the device at an entry port in the bore of the scanner of the MRI machine.
Finally, the invention includes methods for recycling a chosen gas through the use of any of the devices described herein.